Electrowetting display device with stable display states

ABSTRACT

An electrowetting display device comprising a first support plate including: a surface; and a first electrode, a second support plate; and a protrusion having a protrusion surface. The protrusion is formed as part of at least one of the first or second support plates. The protrusion has an elongate shape extending from one to the other of the first or second support plates. The device further comprises a first fluid adjoining at least one of the protrusion surface or the surface of the first support plate; a second fluid immiscible with the first fluid; a second electrode in electrical contact with the second fluid; and a third electrode.

BACKGROUND

Electrowetting display devices are known. A configuration of a first andsecond fluid influences a display effect provided by a display elementin such a device. It is known for backflow to occur. Backflow is where,despite applying a voltage for maintaining a configuration of thefluids, for example due to a capacitance of the display element, theconfiguration changes towards a configuration corresponding to thatwhere no voltage is applied. This change of fluid configuration isproblematic for displaying a desired display effect. Examples of knowntechniques for managing backflow include periodically applying a resetpulse.

It is desirable to overcome problems caused by backflow.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A, 2A and 3A show schematically a cross-section of an exampleelectrowetting element;

FIGS. 1B, 2B and 3B show a plan view of the example electrowettingelement;

FIG. 4 shows schematically circuitry for controlling the exampleelectrowetting element;

FIG. 5 shows schematically a method for controlling the exampleelectrowetting element;

FIG. 6 shows schematically an alternative example of circuitry forcontrolling the example electrowetting element;

FIGS. 7 and 8 show schematically in cross-section another example of anelectrowetting element;

FIGS. 9 and 10 show schematically in cross-section a further example ofan electrowetting element;

FIG. 11 shows schematically a system diagram of an example apparatusincluding an electrowetting display device;

FIG. 12 shows a method of controlling an electrowetting display device,according to examples; and

FIG. 13 shows a method of manufacturing according to examples.

DETAILED DESCRIPTION

Examples will be described of an electrowetting display device having aprotrusion. Although specific examples are described with reference tothe FIGS., it is to be appreciated that further examples are envisagedwhich, although they may have some features in common with the examplesof the FIGS., may have further features than those described using theFIGS. Therefore, specific examples described using the FIGS. are not tobe taken as limiting and, as the skilled person will understand, certainfeatures of examples described with the FIGS. are not limited to thespecific implementation of the example of a FIG., but may be used and/oradapted for a different example, within the scope of the appendedclaims. For example, a shape of an electrode described below, awettability of a surface for the first fluid or the second fluid and/ora thickness of an insulator or layer of material for example having ahydrophobic surface may be tuned to control motion of fluid within thedisplay element.

Examples of an electrowetting display device will now be described. Suchdevices include a first support plate with a surface and a protrusionwith a surface, otherwise referred to as a protrusion surface. Using anapplied voltage, a first fluid is transferrable from at least partlyadjoining the surface of the protrusion to at least partly adjoining thesurface of the first support plate, and vice versa. Thus, the firstfluid is switchable between different configurations, for examplebetween: a configuration with a first volume of the first fluidadjoining the surface of the protrusion and a second volume of the firstfluid adjoining the surface of the first support plate; and aconfiguration with a third volume (less than the first volume) adjoiningthe surface of the protrusion and a fourth volume (greater than thesecond volume) adjoining the surface of the first support plate. Thesedifferent configurations correspond with different display effects, forexample having different greyscale levels, as will be explained furtherbelow.

FIG. 1A shows a diagrammatic cross-section of part of examples of anelectrowetting device. In this example the device is an electrowettingdisplay device 1 including a plurality of electrowetting elements, whichare picture elements 2, otherwise referred to as display elements, oneof which is shown in FIG. 1A. In examples, a plurality of electrowettingelements may define a pixel for providing a display effect, eachelectrowetting element of the plurality being a sub-pixel for providinga sub-pixel display effect. In other examples each electrowettingelement may define a pixel. The lateral dimension of the picture elementof the present example is indicated in FIG. 1A by two dashed lines 3, 4.The picture elements comprise a first support plate 5 and a secondsupport plate 6. The support plates may be separate parts of eachpicture element, but the support plates may be shared in common by theplurality of picture elements. The support plates may include a glass orpolymer substrate 8, 10 and may be rigid or flexible. The support platesin examples include further layers and/or structures than illustrated,for example circuitry for controlling the display elements. Suchfeatures are not illustrated in FIG. 1A, for example, for clarity.

The display device has a viewing side 12 on which an image or displayeffect can be viewed and a rear side 14. In FIG. 1A a surface of thesecond support plate 6, which surface is in this example a surface ofthe substrate 10, defines the rear side 14; a surface of the firstsupport plate 5, which surface is in this example a surface of thesubstrate 8, defines the viewing side 12. The display device of FIG. 1Amay have a reflective functionality, for example with the second fluidbeing reflective, as will be described further below. However, furtherexamples are envisaged which comprise a protrusion in accordance withexamples described herein, and which may instead be of the transmissiveor transflective type. A transmissive type of display element can beconsidered to emit light, for example by transmitting light through thedisplay element from a light source to a viewing side. The plurality ofdisplay elements may be monochrome. For a colour display device thedisplay elements may be divided in groups, each group having a differentcolour; alternatively, an individual display element may be able to showdifferent colours. For a colour display device, at least one of thedisplay elements comprises a colour filter, for example a suitable layerwithin the first support plate, for imparting light transmitted throughthe colour filter with a predetermined hue for a required displayeffect.

A space 16, which may otherwise be considered to be a chamber, of eachdisplay element between the support plates is filled with two fluids,which in this example are liquids. In the example of FIG. 1A, the space16 is filled with a first fluid 18 and a second fluid 20. Therefore thefirst and second fluids are located between the first and second supportplates.

The second fluid is for example at least one of electrically conductiveor polar and may be water or a salt solution such as a solution ofpotassium chloride in water. “Electrically conductive” for example meansthat the second fluid is capable of conducting electricity; for examplean electrical current may flow through the second fluid due to the flowof ions for example through the second fluid. “Polar” in examples meansthat the second fluid comprises at least one compound (for example aliquid vehicle) having a molecule with a net dipole; i.e. that acrossthe molecular structure the molecule has an overall dipole moment, dueto an electron distribution, with at least one part of the moleculehaving a negative electrical charge and at least one different part ofthe molecule having a positive electrical charge. Such dipole momentsinclude permanent dipoles. The polarity is caused for example by thepresence of one or more atom to atom bond in the molecule, with forexample one of the atoms being a heteroatom such as oxygen or nitrogen.For example, such a polar atom to atom bond is a bond between an oxygen(O) atom and a hydrogen (H) atom, i.e. an —O—H bond, which may be insome examples due to the presence of at least one hydroxyl (—OH) group.The presence of such bonds may cause hydrogen bonding between differentmolecules within the second fluid.

The second fluid in the example of FIG. 1A is substantially reflective,for example the second fluid is configured to reflect at least 50% ofvisible light incident on the second fluid, for example, at least 60%,at least 70%, at least 80%, at least 90%, at least 95%, approximately100% or 100% of visible light. The reflectivity of the second fluid mayin examples be provided by white pigment particles dispersed andsuspended in a carrier liquid (such as water or the salt solutiondescribed above). The white pigment particles may for example betitanium dioxide or an alternative white pigment compatible with acarrier liquid which is suitable for use in an electrowetting displayelement. In other examples, the second fluid may be transparent and maybe coloured and/or absorbing.

The first fluid is at least one of non-polar or electricallynon-conductive and may for instance be an alkane like decane orhexadecane or may be an oil such as silicone oil.

The second fluid is immiscible with the first fluid. Therefore, thefirst fluid and the second fluid do not substantially mix with eachother and in some examples do not mix with each other to any degree. Thesubstantial immiscibility of the first and second fluids is due to theproperties of the first and second fluids, for example their chemicalcompositions; the first and second fluids tend to remain separated fromeach other, therefore tending not to mix together to form a homogeneousmixture of the first and second fluids. Due to this immiscibility, thefirst and second fluids meet each other at an interface 22, whichinterface defines a boundary between the volume of the first fluid andthe volume of the second fluid; this interface or boundary may bereferred to as a meniscus. With the first and second fluidssubstantially not mixing with each other, it is envisaged in someexamples that there may be some degree of mixing of the first and secondfluids, but that this is considered negligible in that the majority ofthe volume of first fluid is not mixed with the majority of the volumeof the second fluid.

The first fluid absorbs at least a part of the optical spectrum. Thefirst fluid may be transmissive for a part of the optical spectrum,forming a colour filter. For this purpose the first fluid may becoloured by addition of pigment particles or a dye. Alternatively, thefirst fluid may be black, for example absorbing for substantially allparts of the optical spectrum, or reflecting. In examples to bedescribed herein, the first fluid is black and therefore absorbssubstantially all parts of the optical spectrum, for example in thevisible light spectrum. The term “substantially absorbs” includes adegree of variation, therefore the first fluid may not absorb allwavelengths, but the majority of wavelengths within a given spectrumsuch as the visible spectrum, so as to perform the function of the firstfluid in the element. The first fluid is therefore configured to absorbsubstantially all light incident on the first fluid. For example thefirst fluid may absorb 90% or more of light in the visible spectrum andincident on the first fluid.

In examples, such as that of FIG. 1A, the first support plate 5 includesan insulating layer 24. The insulating layer is transparent. Theinsulating layer 24 may extend between walls of a picture element. Toavoid short circuits between the second fluid 20 and electrodes arrangedunder the insulating layer, layers of the insulating layer may extenduninterrupted over a plurality of picture elements 2, as shown in FIG.1A. The insulating layer has a surface 26 facing the space 16 of thepicture element 2. The surface 26 is therefore a surface of the firstsupport plate at least partly adjoined by at least one of the first orsecond fluids, which surface provides a display area over which adisplay effect is controlled. The thickness of the insulating layer maybe less than 2 micrometres and may be less than 1 micrometre.

In examples, the insulating layer may be a single layer, for exampleformed of a hydrophobic material; alternatively, as shown in FIG. 1A, itmay include a hydrophobic layer 28 and a barrier layer 30 withpredetermined dielectric properties, the hydrophobic layer 28 facing,for example closest to, the space 16, as shown in FIG. 1A. Thehydrophobic layer is schematically illustrated in FIG. 1A and may beformed of Teflon® AF1600. The barrier layer 30 may have a thickness,taken in a direction perpendicular the plane of the substrate, between50 nanometres and 500 nanometres and may be made of an inorganicmaterial like silicon oxide or silicon.

Each display element 2 includes an electrode 32 as part of the firstsupport plate 5, otherwise referred to herein as the first electrode.The electrode is associated with, for example overlaps, the surface ofthe support plate providing the display area. In examples shown there isone such electrode 32 of the first support plate per display element.The electrode 32 is separated from the fluids by the insulating layer24; electrodes of neighbouring picture elements are each separated fromeach other by a non-conducting layer.

In some examples, further layers may be arranged between the insulatinglayer 24 and the electrode 32. The electrode 32 can be of any desiredshape or form. The electrode 32 of a picture element is supplied with anelectrical potential signal by a signal line 34, schematically indicatedin FIG. 1A. A second signal line is connected to an electrode 36(referred to herein as a second electrode) that is in electrical contactwith the second fluid 20, so that charge can flow from the electrode tothe second fluid. This electrode may be common to all elements, whenthey are fluidly interconnected by and share the second fluid,uninterrupted by walls.

In examples, for example that of FIG. 1A, the first fluid 18 is confinedto adjoin a display area of the display element by at least one wall, inthis example walls 38 that follow the cross-section of the pictureelement. The cross-section of a picture element may have any shape; whenthe picture elements are arranged in a matrix form, the cross-section isusually square or rectangular, but in other examples differentcross-sectional shapes are envisaged. It is noted that although inexamples described a plurality of walls follow the cross-section of thepicture element and confine the first fluid to adjoin the display area,in other examples there may be one continuous wall surrounding thedisplay area.

Although the walls are shown as structures protruding from theinsulating layer 24, they may instead be a surface layer of the supportplate that repels the first fluid, such as a hydrophilic or lesshydrophobic layer. The walls may extend from the first to the secondsupport plate but may instead extend partly from the first support plateto the second support plate as shown in FIG. 1A. The dimension of thepicture element, indicated by the dashed lines 3 and 4, is defined bythe centre of the walls 38. The area of the surface 26 between the wallsof a picture element, indicated by the dashed lines 40, 42, is calledthe display area 44, over which a display effect occurs and which isadjoined by the first fluid where the surface is not also adjoined bythe protrusion described later. The display effect depends on a size ofarea that the first and second fluids adjoin the surface defined by thedisplay area, in dependence on the magnitude of an applied voltage V aswill be described in due course. The magnitude of a voltage V appliedbetween the first and second electrodes 32, 36 and between third andsecond electrodes 32′,36 therefore determines the configuration of thefirst and second fluids within the element and is used to control thefluid configuration.

In examples, such as that of FIG. 1A, the second support plate 6 has asimilar construction to that of the first support plate. Features of thesecond support plate which are similar to those of the first supportplate are labelled in FIG. 1A with the same reference numerals markedwith'. For example, the second support plate comprises an electrode 32′(referred to elsewhere herein as the third electrode) which is similarto the electrode 32 of the first support plate, though in other examplesa shape, the electrical properties and/or the material of the electrodesmay be different for each electrode. In examples, the third electrodeforms part of the second support plate and overlaps the protrusion, forexample a lateral extent of the third electrode overlaps a lateralextent of the protrusion. Descriptions of features of the first supportplate should be taken to apply for the corresponding features of thesecond support plate. Differences between the first support plate andthe second support plate will therefore now be described.

In examples, for example that of FIG. 1A, the display element comprisesa protrusion. In the example of FIG. 1A the protrusion 46 is formed aspart of the second support plate 6 (and hence the bracket in FIG. 1Aextends to include the protrusion 46 but doesn't include the walls 38 ofthe first support plate).

A protrusion described herein is a formation which protrudes from atleast one of the first or second support plates and is formed as part ofat least one of the first or second support plates. In the example ofFIG. 1A the protrusion protrudes from the second support plate andextends to contact the surface 26 of the first support plate. In otherexamples however the protrusion is instead formed as part of the firstsupport plate or as part of both of the first and second support plates.

Many different forms of the protrusion are envisaged for differentexamples. For example, as illustrated in FIG. 1A, but envisaged forother examples too, the protrusion has an elongate shape, for example isan elongate element, which extends from a respective one of the first orsecond support plates to a respective other of the first or secondsupport plates; for example the protrusion extends from the secondsupport plate in a direction substantially perpendicular to a plane ofthe surface 26′, e.g. perpendicular within manufacturing tolerances. Theprotrusion may be considered to be a structure, a post, a column, or apillar, for example. In examples, the protrusion may have a greaterheight than width, though in other examples may be wider than the heightof the protrusion. The protrusion for example occupies less than 50%,for example less than 40%, less than 30%, less than 20% or less than10%, of the surface of the first support plate adjoined by at least oneof the first or second fluids. Therefore, the protrusion occupies, forexample has a footprint covering, a relatively minor area of the surfacefor adjoinment by the first and/or second fluids. A cross-section of theprotrusion, taken in a plane parallel the plane of the surface 26′ ofthe second support plate, is for example circular or square, thoughother shapes are envisaged. Further, a shape and size of such across-section may be substantially constant along the length of theprotrusion, for example constant within acceptable manufacturingtolerances, though in other examples the shape or size may change alongthe length of the protrusion as will be explained with an example usingFIGS. 4 and 5 below. The dimensions of the protrusion are for exampledesigned for the protrusion to sufficiently perform its function forexample as a conduit for guiding flow of the first fluid, as will bedescribed in further detail below. Further, the location of theprotrusion within the lateral extent of the display element may bedifferent for different examples. The location may for example beselected to improve the first fluid conduit properties; for example, theprotrusion may be located substantially centrally relative to thesurface 26′, e.g. central within acceptable manufacturing tolerances, sothat flow of first fluid to and from the display area of the firstsupport plate 5 is uniform around the protrusion. This is an example ofthe protrusion being separated from the at least one wall by at leastone of the first or second fluids; for example laterally from theprotrusion there is at least one of the first or second fluids betweenthe protrusion and the at least one wall. The protrusion may thereforebe located within the display area.

In the example of FIG. 1A, the protrusion 46 is an elongate elementformed on the barrier layer 30′ and located substantially centrallyrelative to the lateral extent of the display element. The protrusion isformed as part of the second support plate. In this example theprotrusion 46 has a circular cross-section. In examples such as that ofFIG. 1A the protrusion extends from the second support plate andcontacts the surface 26 of the first support plate. By contacting thesurface, the protrusion may additionally act as a spacer for reducingdeformation of at least one of the first or second support plates.

In examples, the protrusion may be formed of a single material forexample a hydrophobic material. In other examples, for example that ofFIG. 1A, the protrusion is formed of an elongate structure 48 and ahydrophobic layer 50 covering the elongate structure 48. The elongatestructure is for example formed on a layer of at least one layer of oneof the first or second support plates. The hydrophobic layer 50 forexample also covers a surface of the layer of the at least one of thefirst or second support plates; for example, in FIG. 1A the hydrophobiclayer also covers the insulating layer 30′ of the second support plateand therefore is a continuous hydrophobic layer of the second supportplate which provides the surface 26′ of the second support plate and asurface of the protrusion 52 for adjoinment by at least one of the firstor second fluids. Thus in FIG. 1A, the protrusion is formed as part ofthe second support plate. The hydrophobic layer in examples has asubstantially uniform thickness, for example uniform within acceptablemanufacturing tolerances.

In examples, the surface of the protrusion is formed of a material whichhas a lower wettability for the first fluid than the surface of thefirst support plate without a voltage applied. Therefore, in FIG. 1A,the surface of the protrusion 52 is less wettable for the first fluidthan the surface 26 of the first support plate without a voltageapplied; as will be explained more later, this means the first fluid isswitchable to adjoin the surface of the protrusion and/or the surface ofthe first support plate. The surface of the protrusion in examples liesout of the plane of the surface 26′ of the second support plate;therefore, for example, a surface of the protrusion could be consideredto lie in a plane which is perpendicular to a plane of the surface ofthe second support plate.

It is to be noted that a wettability of a surface of a material maychange when a voltage is applied across the surface, due to anelectrowetting effect on the surface of the material. Therefore,although the inherent wettability property of the material does notchange with or without application of a voltage, the wettability of thesurface of the material may temporarily change, when a voltage isapplied across the surface, from the inherent wettability to a differentwettability which for example is less wettable for the first fluid andis therefore for example more wettable for the second fluid. At variouspoints below in the description therefore, a wettability of a surface isreferred to in the context of no or without a voltage being applied;this intends to describe an inherent wettability property of thematerial having the surface, without the influence of the electrostaticcharge on the surface.

Wettability relates to the relative affinity of a fluid for a surface ofa solid. Wettability may be measured by the contact angle between thefluid and the surface of the solid. The contact angle is determined bythe difference in surface tension between the fluid and the solid at thefluid-solid boundary. For example, a high difference in surface tensioncan indicate hydrophobic properties. In examples described herein, asurface which is wettable by the first fluid forms a contact angle atthe fluid-solid boundary within the range 1 to 119 degrees, the anglebeing represented by an arc drawn within the first fluid (not shown).

Despite the surface of the protrusion (for example surface 52 in FIG.1A) being less wettable for the first fluid than the surface of thefirst support plate (for example surface 26 of FIG. 1A), both thesurface of the first support plate and the surface of the protrusion areeach for example wettable by the first fluid, without a voltage applied,and for example are each hydrophobic (with a tendency to repel towater). The wettability of the surface of the protrusion, thewettability of the surface of the first support plate and therefore thedifference in wettability therebetween is selected to enable control oftransferring first fluid between adjoining the surface of the protrusionand the surface of the first support plate and to enable a configurationof the first and second fluids to remain substantially maintained afterapplication of a voltage. This will be explained in further detailbelow.

In examples with the second support plate comprising the protrusion, forexample that of FIG. 1A, a surface of the second support plate foradjoinment by at least one of the first or second fluids comprises thesurface of the protrusion 52 and a further surface 54. The furthersurface is for example formed of a material which has for example,without a voltage applied, a lower wettability for the first fluid thanthe surface of the protrusion and may in some examples be hydrophilic.The further surface is for example part of the surface 26′ of the secondsupport plate but having a lower wettability for the first fluid withouta voltage applied such that the first fluid tends not to wet the furthersurface. The further surface in FIG. 1A for example surrounds andadjoins an other part of the surface 26′ of the second support platewhich adjoins the surface of the protrusion 52. Thus, a line L formedwhere the further surface 54 adjoins the other part of the surface 26′of the second support plate delimits, for example marks, an extent ofadjoinment of the surface of the second support plate which is wettableby the first fluid. In other words, the line L indicates the change ofwettability between the further surface 54 and the surface 26′ of thesecond support plate which limits, for example prevents or blocks, thefirst fluid from spreading across more of the surface of the secondsupport plate than desired. The line therefore for example acts as aperimeter of an extent of the surface of the second support plate whichis wettable by the first fluid. For example, the line L defines amaximum extent of the surface of the second support plate that can bewet by the first fluid. In examples, for example that of FIG. 1A, thefurther surface 54 is hydrophilic whereas the other part of the surfaceof the second support plate is hydrophobic. The surface of theprotrusion adjoining the other part of the surface of the second supportplate has for example the same wettability for the first fluid as theother surface. The surface of the protrusion and the other part of thesurface of the second support plate therefore for example form a singlesurface with the same wettability for the first fluid.

The line may be linear or non-linear, for example circular so as tosurround a lateral extent of the protrusion. The location of the line Lcan be selected when designing an electrowetting display device inaccordance with for example at least one of the volume of the firstfluid, the dimensions of the space for example or the desired switchingproperties of the fluids. Therefore in different examples the positionof the line L may be different than shown in FIG. 1A. For example, thefurther surface may adjoin the surface of the protrusion without anotherpart of the surface of the second support plate in between; an exampleof such an example is described later using FIGS. 6 and 7. With thefurther surface adjoining the surface of the protrusion, the surface ofthe second support plate and therefore the further surface may forexample in some examples have the same wettability as the surface of theprotrusion. In other examples, the further surface may have a greaterwettability to the first fluid than the wettability of the surface ofthe protrusion and may for example be hydrophobic; in such examples thesurface of the protrusion may be hydrophobic or in some exampleshydrophilic.

In other examples, there may be no such further surface. Instead, asurface of the second support plate comprises the surface of theprotrusion and extends from the protrusion to the at least one wall 38′which surrounds the protrusion. For example, a surface of the at leastone wall 38′ of the second support plate which is closest to theprotrusion has, without a voltage applied, a lower wettability for thefirst fluid than the surface of the second plate. For example, thesurface of the at least one wall may be hydrophilic and the surface ofthe second support plate excluding the surface of the at least one wallis hydrophobic. A line where the surface of the at least one wall meets,for example adjoins, the surface of the second support plate thereforeacts in a similar manner as the line L described previously, by limitingan extent of spreading of the first fluid on the surface of the secondsupport plate.

FIG. 1B shows a matrix of rectangular picture elements in a plan view ofthe first support plate. The dimension of the central picture element inFIG. 1B, corresponding to the dashed lines 3 and 4 in FIG. 1A, isindicated by the dashed line 56. Line 58 indicates the inner border of awall; the line is also the edge, for example a perimeter, of the displayarea 26. A dashed line 60 indicates the lateral extent of the protrusion46.

Referring to FIGS. 1A and 1B, an area of adjoinment of the surface 26 ofthe first support plate by the first fluid 18 is shown by the diagonalhatching. Therefore, the perimeter of the first fluid adjoining thesurface 26 of the first support plate is shown by line 62. As will beappreciated, with the first fluid adjoining less than all of the displayarea, where the first fluid is for example black as explained above,light may pass into the display element through the viewing side 12, bereflected by the second fluid, and then exit through part of the displayarea of the first support plate not adjoined by the first fluid.Depending on the size of area of the display area adjoined by the firstfluid, a different display effect may be provided by the displayelement, depending on the amount of light which can exit the displayelement through the display element. Thus, the controllableconfiguration of the first fluid, is used to operate the display elementas a light valve, providing a display effect over the display area.

Examples of controlling a configuration of the first and second fluids,for controlling a display effect provided by the display element, willnow be described further. FIG. 12 also illustrates a method ofcontrolling an electrowetting display device according to examplesdescribed herein.

In examples, the configuration of the first and second fluids isswitchable using a voltage applied between at least one of the first,second or third electrodes. Thus, a volume of the first fluid adjoiningthe protrusion surface and a volume of the first fluid adjoining thesurface of the first support plate is controllable by controlling amagnitude of a first voltage applied between the first and secondelectrodes and by controlling a magnitude of a second voltage appliedbetween the third electrode and the second electrode. The configurationof the first and second fluids illustrated using FIGS. 1A and 1B is oneexample. Further configurations of the first and second fluids areobtainable in dependence on application of at least one of a firstvoltage V1 between the first and second electrodes or a second voltageV2 between the third and second electrodes. This will now bedemonstrated with reference to FIGS. 2A, 2B, 3A and 3B.

FIGS. 2A and 3A show the same display element as FIG. 1A except with adifferent configuration of the first and second fluids. The same is truefor FIGS. 2B and 3B showing the same display element as FIG. 1B. Thesame reference numerals are therefore used in these FIGS.

FIGS. 2A and 2B show an example of a first configuration of the firstand second fluids. This configuration in this example corresponds with abrightest display effect providable by the display element. In otherwords, the first fluid is configured to adjoin a minimum area of thedisplay area (within switching parameters controlled by a display devicecontrol subsystem for example, described later). This is shown by FIG.2B by the diagonal hatching.

FIGS. 3A and 3B show an example of a second configuration of the firstand second fluids. This configuration in this example corresponds with adarkest display effect providable by the display element. In otherwords, the first fluid is configured to adjoin a maximum area of thedisplay area. This is shown by FIG. 3B by the diagonal hatching.

In examples, for example that of FIGS. 1A to 3B, with the first andsecond fluids being in the first configuration, a first volume of thefirst fluid adjoins the surface 52 of the protrusion and a second volumeof the first fluid adjoins the surface 26 of the first support plate;and with the first and second fluids being in the second configuration,a third volume of the first fluid adjoins the surface 52 of theprotrusion and a fourth volume of the first fluid adjoins the surface 26of the first support plate. The third volume is less than the firstvolume and the fourth volume is greater than the second volume. Thefirst fluid in examples may also adjoin further of the surface of thesecond support plate than the protrusion surface.

By controlling application of the first and second voltages, for exampleat least one of the magnitude or the duration of applying the firstvoltage and/or the second voltages, the first fluid is transferrablebetween adjoining a part of the surface of the protrusion and adjoininga part of the surface of the first support plate. Thus, the first andsecond fluids are switchable between the first and secondconfigurations.

It is noted that where the first fluid is described as adjoining asurface, or a part of a surface, this refers to a part of the firstfluid which is on the relevant surface; “on” is not limited for exampleto adjoining the surface but also to a further volume of the first fluidwhich itself does not adjoin the surface but which is supported on therelevant surface.

As explained above, the difference between the wettability of thesurface of the protrusion and the surface of the first support plate isselected to enable control of transferring the first fluid. For example,with the surface of the protrusion having a lower wettability for thefirst fluid than the surface of the first support plate, the first fluidmay have a preference to wet the surface of the first support plate overwetting the surface of the protrusion. However, with both the surface ofthe protrusion and the surface of the first support plate having awettability for the first fluid, without an applied voltage for thefirst fluid, a configuration with part of the first fluid adjoining thesurface of the first support plate and part of the first fluid adjoiningthe surface of the protrusion, remains substantially unchanged afterapplication of the first and/or second voltages, for example afterremoving at least one of the first or second voltages, for examplewithout a voltage being applied between anyone of the first, second orthird electrodes. Substantially unchanged for example is where thedisplay effect from the configuration of first and second fluids isperceived as unchangeable by a viewer. This unchanged display effect maycontinue until a different configuration of the first and second fluidsis required for a different display effect. The configuration maytherefore remain unchanged for longer than a time taken in known devicesfor an oil to move due to backflow. The period of time which theconfiguration may remain unchanged for may in examples be in the orderof days, weeks, months or longer. In this way, the display element maybe considered to provide multiple stable display states for which theconfiguration of the first and second fluids remains substantiallyunchanged without for example the problem of backflow occurring. Thistherefore obviates the need to use backflow reducing or compensatingtechniques known from the art, some of which may use power to implement,for example periodically applying a reset signal.

To change the configuration of the first and second fluids, for exampleto move first fluid from adjoining the surface of the protrusion toadjoin the surface of the first support plate, the first voltage V1,which is applied between the first electrode and the second electrode,is set with a lower magnitude, for example a zero magnitude (i.e.V1=0V), than the second voltage V2 (with a non-zero magnitude) which isapplied between the second electrode and the third electrode. Thiscovers the possibility that the second voltage V2 may be set with agreater magnitude than the first voltage V1. Thus, for example, thefirst and second fluids can be switched from the first configuration (asshown for example in FIG. 2A) to the second configuration (as shown forexample in FIG. 3A). The specific magnitude and duration of applyingeach of the first and second voltages is selected to enable theswitching between fluid configurations, in dependence on the parametersof the display element, for example the wettabilities of the surface ofthe protrusion and the surface of the first support plate and thevolumes of first fluid and second fluid in the display element.

To change the configuration of the first and second fluids, for exampleto move first fluid from adjoining the surface of the first supportplate to adjoin the surface of the protrusion, the first voltage V1 isset with a greater magnitude (a non-zero magnitude) than the secondvoltage V2 which for example has a zero magnitude (i.e. V2=0V). Thiscovers the possibility that the second voltage V2 may be set with alesser magnitude than the first voltage V1. The specific magnitude andduration of applying the first and second voltages is similarlydependent on display element parameters as explained earlier. A zerovoltage is equivalent to not applying a voltage, for example withoutapplication of a voltage between two electrodes.

Thus, by appropriate control of setting the first and second voltages,the first and second fluids can be selectively switched to one of thefirst and second configurations. Moreover, with appropriate selection ofthe magnitude of and the duration of applying at least one of the firstor second voltages, a rate of switching a configuration of the first andsecond fluids, involving transferring the first fluid from a respectiveone to a respective other of the surface of the protrusion and thesurface of the first support plate, may be controlled, for example witha predetermined or preset rate of switching the configuration of thefirst and second fluids.

With appropriate application of at least one of the first or secondvoltages, the first fluid can be considered to be pushed away fromeither the surface of the protrusion or the surface of the first supportplate. The surface of the protrusion can therefore be considered to actas a reservoir for the first fluid. Depending on the magnitude of thefirst and second voltages, a voltage gradient may be set up in favour ofa direction of movement of the first fluid (e.g. from the protrusion tothe first support plate or vice versa). The magnitude of the gradientand therefore the rate of first fluid flow depends for example on thespecific magnitude of each of the first and second voltages.

In examples, to assist “pushing” of the first fluid to the desiredsurface, the voltage with greater magnitude should in examples beapplied across the first fluid. Therefore, for transferring the firstfluid from the protrusion to the surface of the first support plate, thefirst fluid in the first configuration may be located between the secondfluid (to which an electric potential is applied by the secondelectrode) and the third electrode. Thus, the line L delimiting theextent of spreading of the first fluid on the surface of the secondsupport plate may be located between the second fluid and the thirdelectrode so that the second voltage can be applied across part of thefirst fluid. With the second voltage being appliable across the line Lfor example, a force for moving the first fluid is applied at theinterface of the first and second fluids with the surface of the secondsupport plate. Therefore, the force is applied at the edge of the volumeof the first fluid to assist pushing the first fluid towards the surfaceof the first support plate.

As explained above, examples described herein exhibit multiple stableconfigurations of the first and second fluids. This is possible forexample by at least one memory and computer program instructions beingconfigured to, with at least one processor substantially maintain one ofthe first or second configuration of the first and second fluids until adifferent configuration of the first and second fluids is required forproviding a different display effect. This is done for example bywithholding, for example not, applying a voltage, such as a furtherfirst voltage, between the first and second electrodes and withholdingapplying a voltage, for example a further second voltage, between thethird electrode and the second electrode, during a period betweenapplying the first voltage and applying the second voltage to set onefluid configuration and then applying the further first voltage and thefurther second voltage to switch the first and second fluids to adifferent configuration.

Further details of circuitry for controlling switching of theconfiguration of the first and second fluids will now be described.

FIG. 4 shows schematically an example of parts of a system such as aportable apparatus 70. Further details of such an example are explainedfurther below. The apparatus includes an electrowetting display devicesuch as that described in examples above. The electrowetting displaydevice comprises a plurality of a display element of an exampledescribed herein with a protrusion. Therefore each respective displayelement of the plurality of display elements, for example at least afirst display element and a second display element, comprises arespective one of: the surface of the first support plate, the surfaceof the second support plate, the protrusion, the first fluid, the secondfluid, the first electrode and the third electrode.

In this example the plurality of display elements are arranged in amatrix layout and are controlled using a so-called active matrix drivingtechnique as the skilled person will appreciate. It is to be appreciatedthat in other examples a passive matrix technique may be used, againknown to the skilled person, for example with a dedicated driver perdisplay element for applying a voltage to that display element. In suchexamples the display area may correspond with a segment of an imagedisplayable by the device.

Returning to the examples using active matrix driving, for example asshown in FIG. 4, each of the first and second support plates includeactive matrix circuitry for controlling applying the first and secondvoltages V1, V2 respectively. There is a display driving system and adisplay device such as the electrowetting display device describedabove. The display driving system is for example part of a displaydevice control subsystem described later and in this example includes adisplay controller or controller 72, a display row driver 76 for thefirst support plate and a display column driver 74 for the first supportplate. Data indicative of display states of the display elements, thedisplay states for example representing a still image or video images,for example display effects, is received via an input line 78 to thedisplay driving system. The display controller includes at least oneprocessor 80 for processing the data received via the input line 78. Theprocessor is connected to at least one memory 82. The display controllerprepares the data for use in the display device. The at least one memorymay store computer program instructions that are configured to cause thedisplay apparatus to perform one or more of the methods of controlling adisplay device as described when being executed by the processor. Thecomputer program instructions may be stored on a computer programproduct including a non-transitory computer-readable storage medium. Anoutput of the processor 80 is connected by line 84 to the display rowdriver 76, which includes row driver stages 86 that transform signals tothe appropriate voltages for the display device. Row signal lines 88connect the row driver stages to respective rows of the display devicefor transmitting the voltage pulses generated in the display row driverto display elements in each row of the display device, thereby providinga row addressing signal to each row of the display device. In otherwords, one or more voltage pulses for addressing one or more rows istransmitted over the row signal lines 88 corresponding to the rows toswitching elements corresponding respectively to the display elements inthe one or more rows. The display row driver 76 generates the voltagepulses used for addressing the rows of the display device, usinginformation from the processor 80 to set a value of the pulse durationof the voltage pulses. Another output of the processor 80 is connectedby line 90 to the display column driver 74, which includes column driverstages 94 that transform signals to the appropriate voltages for thedisplay device. Column signal lines 92 connect the column driver stagesto the columns of the display device, providing a column signal to eachcolumn of the display device. The display controller 72 determines whichrows are selected for addressing and in which order. The selected rowsare consecutively addressed by applying an addressing signal to each ofthese rows.

The addressing may include the steps of determining a value for a firstpulse duration corresponding to at least one voltage pulse to be appliedto a row of display elements, generating the at least one voltage pulsehaving the first pulse duration and transmitting the at least onevoltage pulse to the rows to be addressed. In examples where the displayelements of a row are connected to the same row signal line, addressinga row means addressing each display element of that row. When a displayelement is being addressed, the display element admits the column signalthat is applied to the column signal line to which the display elementis connected. The column signal for a display element is appliedsubstantially simultaneously with the voltage pulse used for addressingthe display element. Substantially simultaneously means for example thatthe column signal is present on the column signal line for at least thepulse duration of the voltage pulse. The display drivers may comprise adistributor, not shown, for distributing data input to the displaydriver over a plurality of outputs connected to the driver stages. Thedistributor may be a shift register. FIG. 4 shows the signal lines onlyfor those columns and rows of the display device that are shown in theFIG. The row drivers may be integrated in a single integrated circuit.Similarly, the column drivers may be integrated in a single integratedcircuit. The integrated circuit may include the complete driverassembly. The integrated circuit may be integrated on the substrate 8 orthe substrate 10 of the display device. The integrated circuit mayinclude part or the entire display device control subsystem. The displaydevice comprises a plurality of display elements arranged in a matrix ofn rows, where n may be ≧2, i.e. larger than one. The matrix may have anactive matrix configuration. The matrix may have m columns, where m maybe ≧2; the total number of display elements in this example is n×m. FIG.4 shows display elements for five rows, labelled k to k+4 and fourcolumns labelled l to l+3. The total number of rows and columns forcommon display devices may range between a few hundred and a fewthousand. The display elements, also referred to as pixels in FIG. 4(but which in other examples may be sub-pixels) of column 1 are labelledp to p+4. Each display element may have the same construction as thedisplay element 2 in FIG. 1A. FIG. 4 shows a few electrical parts of thedisplay elements. Each display element of the display device includes anactive element in the form of one or more switching elements. Theswitching element may be a transistor, for example a thin-filmtransistor (TFT), or a diode. The first and second electrodes of thedisplay element are indicated as a pixel capacitor Cp. A line connectingthe second electrode of the capacitor to ground is the common signalline (36 of FIG. 1) and the line connecting the first electrode of thecapacitor to the transistor is the signal line 34 shown in FIG. 1. Thedisplay element may include a capacitor Cs for storage purposes or formaking the duration of the holding state or the voltage applied to theelement uniform across the display device. This capacitor is arranged inparallel with Cp and is not separately shown in FIG. 3. The columndrivers provide the signal levels corresponding to the input data forthe display elements. The row drivers provide the signals for addressingthe row of which the elements are to be set in a specific display state.In examples, addressing a row means applying a signal on the signal lineof the row that switches a transistor of each of the display elements ofthe row to a conducting state of the transistor. Each row of the n rowsof the display device is addressable by a signal such as a voltagepulse; the voltage pulse is applied to a switching element of each ofthe display elements in the addressed row for switching the switchingelement.

The addressing of rows is part of the addressing of display elements inan active matrix display device. A specific display element is addressedby applying a voltage to the column in which the specific displayelement is located and applying a voltage pulse to the row in which thespecific display element is located. When the transistor of a displayelement receives at its gate a voltage pulse of its row addressingsignal, the transistor becomes conducting and it passes the signal levelof its column driver to the electrode 32 of the display element. Inexamples, a voltage pulse is a rapid, transient change in the voltagefrom a baseline value to a higher or lower value, followed by a rapidreturn, for example a change, to the baseline value. The time periodbetween the two subsequent voltage changes of the voltage pulse iscalled a pulse duration. After the transistor has been switched off, sothe transistor is no longer conducting, the voltage over the cell willbe maintained within acceptable tolerances until the transistor isswitched on again by the next row addressing signal for the displayelement. In this active matrix driving method the electrodes of theelectrowetting cells are connected to the driving stages briefly at thestart of a period during which they show a certain display effect.During this connection, a voltage related to the desired display effectis applied to the electrodes. After the display element is disconnectedfrom the driver stage, the voltage on the electrodes is maintainedwithin acceptable tolerances by one or more capacitors during the periodduring which the display element shows the display effect. The method iscalled ‘active’, because the display element contains at least oneactive element, for example a transistor.

FIG. 5 shows a diagram of an example method of driving the displayelements in a display device having an active matrix configuration. Themethod displays images during a series of frames, for example, an imageis displayed within the duration of one frame. During a frame alldisplay elements of a display device may be addressed; in a matrix allrows of the matrix of a display device are addressed during a frame.FIG. 5 shows two column signals V1 and V1+1 and five row addressingsignals Vk . . . Vk+4 as a function of time t for two consecutive framesr and r+1. The duration of a frame or frame period is Tf. In examples, aframe period Tf is a pre-determined period for addressing the n rows ofthe matrix. In some examples the frame period is the period betweenconsecutive addressing the same row. The duration of the period may befixed, for example programmed, in the controller 72.

When row k is selected and addressed by a pulse on the row addressingsignal Vk, as shown at the start of frame r in FIG. 5, the transistor ineach display element of row k becomes conducting and the voltages oneach of the column signal lines 92 will be put on the electrode 32 ofeach display element in row k. Subsequently, the display column driver94 of FIG. 4 changes the voltages on the column signal lines to thevalues required for row k+1. When row k+1 is selected by a pulse on rowaddressing signal k+1, the voltages are put on the electrode 32 of FIG.1A of the display elements of row k+1. All n rows of the display devicewill be selected consecutively in a similar manner in frame r. Theprocess of selecting the rows starts again in the following frame r+1.

In examples of common display apparatuses the pulse duration of thevoltage pulse of the row addressing signal, also called the gate periodTg or gate time, is such that the n rows of the display device can beaddressed consecutively within one frame period. Common displayapparatuses have therefore usually a pulse duration equal to or lessthan Tf/n, n being the number of rows. For example, addressing 1000 rowsin a frame period of 20 milliseconds requires a pulse duration of 20microseconds or less.

The active matrix example just described is used for controllingapplication of the first voltage between the first electrode and thesecond electrode. In examples an active matrix type technique is alsoused for controlling application of the second voltage between the thirdelectrode and the second electrode. Therefore, the electrowettingdisplay device includes a second active matrix. This is illustrated inFIG. 4. Many features of the second active matrix are similar to thoseof the active matrix described for controlling application of the firstvoltage. Such features are labelled with the same reference numeral usedpreviously with an added '; corresponding descriptions should be takento apply. For example, the display column driver which corresponds withthe display row driver 74 of the first active matrix describedpreviously is labelled 74′. Thus, a separate display column driver isused for driving the columns of the second active matrix, which receivesdata input via line 98. However, the same display row driver 76 may beused as illustrated in FIG. 4 with lines 96 connecting the row signallines 88 of the first active matrix to the row signal lines 88′ of thesecond active matrix. In this way the first voltage and the secondvoltage may be applied to a display element together, for example theyare synchronised with each other due to, for a given display element,the TFT of each of the first and second active matrices responding toapply the appropriate column signal when the relevant row driver stage86 outputs a row signal.

The example described using FIG. 4 is an example of circuitry forcontrolling the first and second fluid configuration of each displayelement. The circuitry includes for example a matrix of TFTs andconnectors for connecting the display elements to the controller. It isan example of the first support plate comprising first circuitry 71including switching elements (such as a TFT) which are independentlyswitchable for controlling application of the first voltage for at leastone respective display element of the plurality of display elements; andthe second support plate comprising second circuitry 71′ includingswitching elements (such as a TFT) which are independently switchablefor controlling application of the second voltage for at least onerespective display element of the plurality of display elements. Thedisplay element may be any example display element described herein, forexample.

In the example of FIG. 4, the first circuitry is for example at leastpartly mounted on the substrate 8 and the second circuitry is forexample at least partly mounted on the substrate 10. In other examples,part of the second circuitry may be mounted on the substrate 8 of thefirst support plate or vice versa. Therefore, the matrix of TFTs of eachactive matrix may be formed as part of one of the support plates.Therefore one of the first or second support plates includes both thefirst circuitry and the second circuitry, with one of the firstcircuitry or the second circuitry being electrically connectedrespectively to the first electrode of each of the plurality of displayelements or the third electrode of each of the plurality of displayelements. This electrical connection may be via a connection linethrough for example a wall of each display element. This configurationof the circuitry is useful such that fabrication of the circuitry isdone as part of one support plate and is therefore simpler thanfabricating the circuitry on both support plates. Further, a quality ofdisplay effect may be improved if the display effect is not emitted fromthe display elements through a layer of circuitry; in other words, inexamples, the viewing side is not part of a support plate having activematrix circuitry.

FIG. 6 shows schematically a different example of circuitry forcontrolling the application of the first and second voltages, comparedwith the example of FIG. 4. Features described using FIG. 4 are similarto features used in the example of FIG. 6 and are therefore labelledwith the same reference numerals incremented by 200. Correspondingdescriptions should be taken to apply and are not repeated here, forconciseness. The description which now follows will therefore describedifferences from the example of FIG. 4.

In this example, instead of each display element including an individualfirst electrode, the first electrode of each display element of theplurality of display elements is part of a single electrode 100 whichoverlaps the surface of the first support plate of each display element.A separate driver 102 for the first electrode is connected to the line298 for receiving input data for a driver stage 104 to apply the firstvoltage between the second and first electrodes using the line 106connecting the driver stage 104 to the first electrode, which line 106is similar to the line 34 shown in FIG. 1A. The display controller 272is configured for example to control the separate driver for the firstelectrode in coordination with application of the second voltage usingthe active matrix illustrated.

In an example of examples with a single first electrode overlapping theplurality of display elements, the at least one memory and computerprogram instructions are configured to, with the at least one processor,control the electrowetting display device to apply a voltage between thefirst electrode and the second electrode of each of the plurality ofdisplay elements for transferring substantially all of the first fluidfrom the surface of the first support plate to the surface of theprotrusion, for each respective display element of the plurality ofdisplay elements. Substantially all means for example that the displayelement is driven to the first configuration illustrated in FIG. 2A,this being the fluid configuration which the controller is configured todrive the fluids to the brightest display effect. This transfer can beconsidered as a reset of all display elements to prepare the displayelements for then being individually switched to the respective fluidconfiguration for each display element. Then, for example subsequently,after the transferring of substantially all of the first fluid, a secondvoltage with the respective magnitude required for each display elementis applied, for switching the first and second fluids of each respectivedisplay element to a configuration for providing a required displayeffect.

It is noted that FIG. 6 shows the single first electrode as part of thefirst support plate in the lower page of FIG. 6 and that active matrixcircuitry of the second support plate is shown in the upper page of FIG.6. In further examples, instead of a single first electrode, there is anindividual first electrode for each display element; instead, the thirdelectrodes are formed as part of a single electrode of the secondsupport plate with a separate driver, similar to that labelled 102 usedfor applying the second voltage. In further examples, instead of asingle electrode performing the function of the first or thirdelectrodes, the first electrodes or third electrodes of one or many rowsof display elements may be formed as a single electrode. Therefore, forexample, the first support plate may have a plurality of longitudinalelectrodes, for example strip shaped, which extend across multipledisplay elements and which each represent a single row electrodecorresponding to a row of first electrodes, for driving a row of displayelements together. Each longitudinal electrode would be driven by aseparate driver such as that labelled 102. In other examples, the secondsupport plate may instead have a plurality of longitudinal electrodeseach representing a single row electrode corresponding to a row of thirdelectrodes.

Further examples of the electrowetting display device are envisaged.

For example, in examples with the protrusion being formed as part of thesecond support plate, the protrusion may extend from the second supportplate but may not contact the first support plate. This is in contrastto the example of FIG. 1A where the protrusion contacts the firstsupport plate. Such an example will now be described with reference toFIGS. 7 and 8. Features of this example are similar to those describedusing FIGS. 1A to 3B and are labelled with the same reference numeralsincremented by 300. Corresponding descriptions should be taken to applyhere also and they are not repeated here, for conciseness.

Referring to FIG. 7, the protrusion 110 is formed as part of the secondsupport plate, for example on a layer of the second support plate as inFIG. 1A, but with a part 112 of the protrusion closest to the firstsupport plate being separated from the first support plate by at leastone of the first or second fluids. In other words, there is a gapbetween the protrusion and the surface 326 of the first support plate,which gap is occupied by at least one of the first or second fluids. Thepart of the protrusion is therefore not contacting the first supportplate. In such examples, the protrusion is less or not visible by aviewer of a display effect provided by the display element. Therefore, aquality of a display effect is improved. Plus, as a greater area of thesurface of the first support plate is available for light to passthrough, a brighter display effect can be provided. FIG. 7 illustrates asecond configuration of the first and second fluids which correspondswith the second configuration shown in FIG. 3A in that the secondconfiguration in this example is a darkest display effect displayable bythe display element. In this fluid configuration the first fluid adjoinsall of the surface 326 of the first support plate.

In examples, such as that of FIG. 7, the first support plate includes atleast one wall which extends to contact the at least one wall 338′ ofthe second support plate. In this way the at least one wall of the firstsupport plate 305 may function as a spacer 116 between the first andsecond support plates, to reduce deformation of the first and secondsupport plates.

In examples, for example that of FIG. 7, a thickness T of thehydrophobic layer 318 covering the structure 348 of the protrusion 110has a thickness which increases along the protrusion in a direction Daway from the first support plate. Where the hydrophobic layer exhibitsinsulating properties, an increased thickness of the hydrophobic layerexhibits and increased insulating property. Therefore, the insulatingproperty of the protrusion increases in the direction D, which caninfluence how the first fluid moves and where such movement initiateswhen the second voltage is applied to move first fluid from theprotrusion to the surface of the first support plate. For example, itmay be desirable to initiate movement of the first fluid on theprotrusion at a part furthest from the first support plate, so that thefirst fluid tends to move along the protrusion towards the first supportplate.

FIG. 8 shows the example of FIG. 7 but with the first fluid in the firstconfiguration, which corresponds to the first configuration of FIG. 2Ain that it is the brightest display effect of this display element. Inthis example, the first fluid does not substantially adjoin any of thesurface 326 of the first support plate; instead substantially all of thefirst fluid adjoins the surface 352 of the protrusion. The termsubstantially is used here to account for the fact that some negligibledeposits of the first fluid may remain on the surface 326 of the firstsupport plate with the first and second fluids being in the firstconfiguration. In the first configuration therefore in this example thepart 112 of the protrusion closest to the first support plate isseparated from the first support plate by at least the second fluid.With the second fluid being substantially reflective and depending onthe thickness of the layer of second fluid between the protrusion andthe surface of the first support plate, the first fluid adjoining thesurface of the protrusion and/or the surface of the second support platemay not have an influence on the display effect provided by the displayelement. Further, the second fluid may protect underlying first fluidfrom exposure to radiation such as ultraviolet radiation which canbleach a dye compound in the first fluid. Therefore the second fluid canhelp reduce exposure of the first fluid to the radiation and thereforeprolong the lifetime of the first fluid.

In a similar manner as described previously, there may be a line Lbetween the surface of the protrusion 352 and a further surface, bothsurfaces being comprised by the surface of the second support plate. Theline delimits an extent of adjoinment of the surface of the secondsupport plate which is wettable by the first fluid. For example, thesurface of the protrusion is hydrophobic and the further surface ishydrophilic. In such examples, for example that of FIGS. 7 and 8, thethird electrode is comprised by the second support plate and the line islocated between the second fluid and the third electrode. This, asdescribed previously, means that, with appropriate design of the displayelement to locate the line appropriately, a force for moving the firstfluid is applied at the interface of the first and second fluids withthe surface of the second support plate.

Referring to the example of FIG. 7 for example, with the first andsecond fluids being configured in the second configuration, for examplewith substantially all of the first fluid adjoining the surface of thesupport plate, part of the first fluid adjoins the surface of theprotrusion. In this way, smooth movement of the first fluid from thesurface of the first support plate to the surface of the protrusion isobtainable, when switching from the second configuration to the firstconfiguration, for example, as the first fluid already contacts thesurface of the protrusion and does not need first to span a gap to thesurface of the protrusion. Appropriate selection of the volume of thefirst fluid, the size of the gap between the protrusion and the surfaceof the first support plate and other parameters of the display elementenable this functionality. In other examples, in the secondconfiguration, none of the first fluid may adjoin the surface of theprotrusion; however, upon applying the appropriate first and secondvoltages, capillary effects for example may cause the first fluid toadjoin the surface of the protrusion and transfer thereto. Thus, inexamples such as that of FIGS. 7 and 8, a distance between the part 112of the protrusion and the surface of the first support plate 326 is suchthat first fluid is transferrable from adjoining the surface of theprotrusion to adjoining the surface of the first support plate duringswitching between the first configuration and the second configuration.The exact distance between the part of the protrusion and the surface ofthe first support plate in examples will depend on other constructionparameters of the display element, so that transfer of the first fluidover the distance is possible. For example, the distance is set inexamples in dependence on at least one of the following: a wettabilityfor the first fluid of the protrusion surface; a wettability for thefirst fluid of the surface of the first support plate; a volume of thefirst fluid; a magnitude of an applied voltage appliable using at leastone of the first, second or third electrodes; a viscosity of the firstfluid; a surface tension of the first fluid; a viscosity of the secondfluid; or a surface tension of the second fluid. The skilled person willreadily understand how such parameters influence the transferability ofthe first fluid over the distance and therefore how the distance may beset accordingly.

In alternative examples from examples described above, the protrusion isformed as part of the first support plate. An example will now bedescribed using FIGS. 9 and 10. Features of this example are similar tofeatures described previously in other examples. Such features arelabelled with the same reference numerals incremented by 400.Corresponding descriptions should be taken to apply here and are notrepeated, for conciseness.

In examples, with the first support plate including the protrusion, theprotrusion 120 has a part 122 closest to the second support plate andwhich is separated from the second support plate by at least one of thefirst or second fluids, for example at least the second fluid. Theprotrusion is separated from the second support plate by a distance suchthat the first fluid cannot transfer to the second support plate; inexamples the display element is designed, for example by modifyingreducing a wettability for the first fluid of a part of the protrusionclosest to the second support plate, to minimise the size of theseparation whilst still preventing first fluid crossing the separation.Therefore the second support plate can be of a simple construction, forexample a single substrate 410. The second support plate may alsoinclude at least one wall which may be formed as a spacer 124 extendingto contact the first support plate, to reduce deformation of the firstand second support plates. The bracket labelled 126 to indicate thesecond support plate indicates the inclusion of the spacers as part ofthe second support plate. In such examples the second support plate doesnot include any circuitry and therefore is simple to manufacture.

In the example of FIGS. 9 and 10, the first support plate 128 includes asubstrate 408, a barrier layer 430 and a hydrophobic layer 428 whichprovides a surface 426 of the first support plate for adjoinment by atleast one of the first or second fluids. The first support plateincludes in this example at least one wall 438 similar to thosedescribed previously.

In examples with the first support plate comprising the protrusion, theprotrusion is formed for example with a structure formed on a layer ofthe first support plate, for example the barrier layer. A hydrophobiclayer 132 for example covers the structure. Therefore, the surface ofthe first support plate has a wettability for the first fluid and asurface 134 of the protrusion has a wettability for the first fluid, inboth cases where no voltage is applied. As explained previously in otherexamples, the surface of the first support plate 426 for example has agreater wettability for the first fluid than the surface of theprotrusion, with both of those surfaces being formed of a hydrophobicmaterial for example.

In examples, such as that of FIGS. 9 and 10, the surface of theprotrusion comprises a first part. A second part, which provides afurther surface of the protrusion, is located between the first part andthe surface of the first support plate. Without a voltage applied, thefirst part has a greater wettability for the first fluid than the secondpart. The surface of the protrusion in examples lies out of the plane ofthe surface 426 of the first support plate. The first part is forexample the hydrophobic layer 132. The second part 133 is for exampleformed of a hydrophilic material. Thus, where the first part and thesecond part adjoin each other, a line L is formed representing a changeof wettability for the first fluid and which, with the fluids in thefirst configuration shown in FIG. 9, is a limit of the extent of wettingof the first fluid of the surface of the protrusion. In some examples,the second part and therefore the further surface of the protrusion hasan extent which corresponds to a thickness of the first fluid withsubstantially all of the first fluid adjoining the surface of the firstsupport plate, the extent and the thickness being taken in a directionperpendicular to a plane of the surface of the first support plate; thisis illustrated using FIG. 9 which shows a first configuration of thefirst and second fluids corresponding with a brightest display effect ofthe display element, as no (or a negligible amount) of the first fluidadjoins the surface 426 of the first support plate.

In examples such as that of FIGS. 9 and 10 the first electrode 432 issimilar to that described in earlier examples except that it is shapedto surround the third electrode which is part of the first support platetoo. Therefore, in this example, where the protrusion has a circularcross section, the first electrode has a circular cut-out, for example ahole or aperture, at its centre to accommodate the third electrode.There is a layer of non-conductive material (not labelled) between thefirst and third electrodes which electrically insulates the first andthird electrodes from each other. Therefore, in examples such as that ofFIGS. 9 and 10, the first support plate comprises the protrusion and thethird electrode. The third electrode in some examples such as that ofFIGS. 9 and 10 is a third electrode 136 which forms part of theprotrusion 120. For example, as shown in the present example, the thirdelectrode extends substantially along a length of the protrusion; forexample, the third electrode extends along the length of the protrusionuntil the hydrophobic layer 132. The protrusion 120 of the example ofFIGS. 9 and 10 is located substantially centrally as describedpreviously for FIG. 1A for example.

The third electrode is for example formed of a suitable material, forexample indium tin oxide (ITO) which may be used to form the firstand/or third electrode in this and other examples. The third electrodeis for example connected to the controller by the signal line 434′.According to various examples described herein, therefore, the thirdelectrode may form part of at least one of the protrusion, the firstsupport plate or the second support plate. This offers flexibility inthe design of the display element.

In examples with the protrusion comprising the third electrode, forexample that of FIGS. 9 and 10, the first fluid may be transferred fromadjoining the surface of the protrusion to adjoin the surface of thefirst support plate using appropriate application of the first voltagebetween the first and second electrodes and the second voltage appliedbetween the third and second electrodes, similar to techniques describedpreviously with relation to application of the first and secondvoltages. For example, a suitable magnitude and duration of applying thevoltages may be used. For the example of FIGS. 9 and 10, with the firstand second fluids being in the first configuration as shown in FIG. 9,the first fluid may be transferred to adjoin the surface of the firstsupport plate by applying for example a first voltage with a lowermagnitude than the magnitude of the applied second voltage. Once thevoltages are removed, for example are no longer applied, the firstfluid, now in the second configuration as illustrated in FIG. 10,remains in the second configuration. This is because, for example, ofthe presence of the second part 133 which resists wetting by the firstfluid and therefore acts as a barrier for first fluid to move to thefirst part of the surface of the protrusion until appropriate magnitudesof the first and second voltages are applied which are sufficient tomove first fluid over the second part (which may be considered as thefirst fluid jumping over the second part) and onto the first part of thesurface of the protrusion. Thus, with the second part functioning as abarrier, the protrusion can act as a reservoir of first fluid, with theamount of first fluid adjoining the surface of the first support plateand the amount of first fluid adjoining the surface of the protrusionbeing controllable by selectively moving amounts of first fluid over thesecond part, either onto or from the surface of the protrusion.

FIG. 11 shows schematically a system diagram of an example system, forexample apparatus 150, comprising an electrowetting display device suchas any of the examples described above, for example the electrowettingdisplay device described above comprising electrowetting displayelements 2. The apparatus is for example a portable, for example mobile,device such as an electronic reader device such as a so-called“e-reader”, a tablet computing device, a laptop computing device, amobile telecommunications device, a watch or a satellite navigationdevice; the apparatus may alternatively be a display screen forinstallation in any machine or device requiring a display screen, forexample a consumer appliance.

The system diagram illustrates an example of a basic hardwarearchitecture of the apparatus 150. The apparatus includes at least oneprocessor 152 connected to and therefore in data communication with forexample: a display device control subsystem 154, a communicationssubsystem 156, a user input subsystem 158, a power subsystem 160 andsystem storage 162. The display device control subsystem is connected toand is therefore in data communication with the display device. The atleast one processor 152 is for example a general purpose processor, amicroprocessor, a digital signal processor (DSP), an applicationspecific integrated circuit (ASIC), a field programmable gate array(FPGA) or other programmable logic device, a discrete gate or transistorlogic, discrete hardware components, or any suitable combination thereofdesigned to perform the functions described herein. A processor may alsobe implemented as a combination of computing devices, e.g., acombination of a DSP and a microprocessor, a plurality ofmicroprocessors, one or more microprocessors in conjunction with a DSPcore, or any other such configuration. The processor may be coupled, viaone or more buses, to read information from or write information to oneor more memories, for example those of the system storage 162. The atleast one processor may additionally, or in the alternative, containmemory, such as processor registers.

The display device control subsystem 154 for example includeselectrowetting display element driver components, for use in applying avoltage to any of the electrowetting display elements, to addressdifferent such display elements. In examples the electrowetting displayelements are configured according to an active matrix configuration andthe display device control subsystem is configured to control switchingelements such as thin film transistors (TFTs) of the display device 1via circuitry to control the electrowetting display elements. Thecircuitry may include signal and control lines such as those describedabove.

The communications subsystem 156 for example is configured for theapparatus to communicate with for example a computing device via a datanetwork, for example a computer network such as the Internet, a localarea network, a wide area network, a telecommunications network, a wirednetwork, a wireless network, or some other type of network. Thecommunications subsystem 156 may further for example comprise aninput/output (I/O) interface, such as a universal serial bus (USB)connection, a Bluetooth or infrared connection, or a data networkinterface for connecting the apparatus to a data network such as any ofthose described above. Content data as described later may betransferred to the apparatus via the communications subsystem.

The user input subsystem 158 may include for example an input device forreceiving input from a user of the apparatus. Example input devicesinclude, but are not limited to, a keyboard, a rollerball, buttons,keys, switches, a pointing device, a mouse, a joystick, a remotecontrol, an infrared detector, a voice recognition system, a bar codereader, a scanner, a video camera (possibly coupled with videoprocessing software to, e.g., detect hand gestures or facial gestures),a motion detector, a microphone (possibly coupled to audio processingsoftware to, e.g., detect voice commands), or other device capable oftransmitting information from a user to the device. The input device mayalso take the form of a touch-screen associated with the display device,in which case a user responds to prompts on the display device by touch.The user may enter textual information through the input device such asthe keyboard or the touch-screen.

The apparatus may also include a user output subsystem (not illustrated)including for example an output device for providing output to a user ofthe apparatus. Examples include, but are not limited to, a printingdevice, an audio output device including for example one or morespeakers, headphones, earphones, alarms, or haptic output devices. Theoutput device may be a connector port for connecting to one of the otheroutput devices described, such as earphones.

The power subsystem 160 for example includes power circuitry 166 for usein transferring and controlling power consumed by the apparatus. Thepower may be provided by a mains electricity supply or from a battery164, via the power circuitry. The power circuitry may further be usedfor charging the battery from a mains electricity supply.

The system storage 162 includes at least one memory, for example atleast one of volatile memory 168 and non-volatile memory 170 and maycomprise a non-transitory computer readable storage medium. The volatilememory may for example be a Random Access Memory (RAM). The non-volatile(NV) memory may for example be a solid state drive (SSD) such as Flashmemory, or Read Only Memory (ROM). Further storage technologies may beused, for example magnetic, optical or tape media, compact disc (CD),digital versatile disc (DVD), Blu-ray or other data storage media. Thevolatile and/or non-volatile memory may be removable or non-removable.

Any of the memories may store data for controlling the apparatus, forexample components or subsystems of the apparatus. Such data may forexample be in the form of computer readable and/or executableinstructions, for example computer program instructions. Therefore, theat least one memory and the computer program instructions may beconfigured to, with the at least one processor, control a display effectprovided by the electrowetting display device.

In the example of FIG. 11, the volatile memory 168 stores for exampledisplay device data 172 which is indicative of display effects to beprovided by the display device. The processor 152 may transmit data,based on the display device data, to the display device controlsubsystem 154 which in turn outputs signals to the display device forapplying voltages to the display elements, for providing display effectsfrom the display device. The non-volatile memory 170 stores for exampleprogram data 174 and/or content data 176. The program data is forexample data representing computer executable instructions, for examplein the form of computer software, for the apparatus to run applicationsor program modules for the apparatus or components or subsystems of theapparatus to perform certain functions or tasks, and/or for controllingcomponents or subsystems of the apparatus. For example, application orprogram module data includes any of routines, programs, objects,components, data structures or similar. The content data is for exampledata representing content for example for a user; such content mayrepresent any form of media, for example text, at least one image or apart thereof, at least one video or a part thereof, at least one soundor music or a part thereof. Data representing an image or a part thereofis for example representative of a display effect to be provided by atleast one electrowetting element of the electrowetting display device.The content data may include data representing a library of content, forexample a library of any of books, periodicals, newspapers, movies,videos, music, or podcasts, each of which may be represented by acollection of data which represents for example one book or one movie.Such a collection of data may include content data of one type, but mayinstead include a mixture of content data of different types, forexample a movie may be represented by data including at least image dataand sound data.

The skilled person will readily understand examples of techniques whichcan be used to manufacture an electrowetting display device according toexamples described herein. Examples will now be given, but it is to beappreciated that numerous further examples are envisaged.

Examples of a manufacture method are given and refer also to FIG. 13 Anexample method of manufacturing an electrowetting display device willnow be described. The example described focuses on the features of onedisplay element (e.g. that of FIG. 1A) but it is to be appreciated thatthe manufacturing method example applies for a device comprising aplurality of display elements.

A support plate, for example the second support plate, is formed whichcomprises the protrusion. A substrate is provided and then at least onelayer is deposited on the substrate using for example chemical orphysical vapour deposition (CVD or PVD) for example sputter depositionor electron beam evaporation where temperature, pressure and power arecontrolled appropriately, as would be understood by the skilled person.

The at least one layer includes for example at least one electrode and abarrier layer as described previously using FIG. 1A for example. Furtherlayers may also be deposited and patterned to form circuitry forcontrolling the display elements. A layer, for example an electrodeprecursor layer, of the at least one layer is patterned to form theelectrode of for example ITO using an appropriate patterning techniqueas the skilled person would understand. An example of such a patterningtechnique involves masking areas of the electrode precursor layer toremain after the patterning with a photoresist material, using a photolithography technique to harden the photoresist in areas where the atleast one electrode is to be formed, removing the un-hardenedphotoresist and then etching the deposited metal not covered by thephotoresist, for example an acidic etching solution.

A further layer, for example a protrusion precursor layer, is depositedon the at least one layer, for example on the barrier layer, and ispatterned to form at least part of a protrusion on the at least onelayer, the protrusion having an elongate shape extending from the atleast one layer. The protrusion may for example be formed of SU8photoresist and may be patterned using a photolithography process as theskilled person would readily understand. An example of such aphotolithography process involves for example after spreading the SU8photoresist material on the at least one layer, patterning usingultraviolet light applied selectively, using a mask, to the photoresistmaterial. Hard baking is then performed of the photoresist materialwhich is then developed using an appropriate development solution theskilled person would readily be familiar with. In some examples, theprotrusion may now be formed, but in other examples further stages arerequired. For example, the patterning of the further layer is apatterning to form an elongate structure of the protrusion. Then, acoating is applied on part of the at least one layer (for example a partof the barrier layer on which the elongate structure is not formed) andon the elongate structure of the protrusion. This coating has an outersurface which is for adjoinment with at least one of the first or secondfluids of the electrowetting display device. The coating may for examplebe a hydrophobic material, for example Teflon®AF1600, which is forexample applied using a slit coating or spin coating technique which iswell known in the art. In some examples the coating may be applied witha thickness which decreases along a length of the protrusion. The termapplied is used here for the application of the coating compared withthe term depositing used in relation to depositing the at least onelayer, to distinguish in examples between different types of applicationand deposition techniques. For example depositing the at least one layermay use a vapour deposition type of technique in contrast to using a wetprocess for applying the coating (for example spin coating).

In some examples the outer surface of the coating may be treated, forexample to change a property of the outer surface of the coating, forexample to reduce the wettability for the first fluid. This treatmentmay be reactive ion etching (RIE), for example using radio frequencyinitiated plasma, which the skilled person would readily be familiarwith and which can be applied selectively to form parts of a surface ofthe second support plate which are to have a lower wettability for thefirst fluid than other parts (though in other examples differentmaterials may additionally or instead be applied which have differentwettability properties, for forming surfaces with different wettabilityproperties). After the coating has been applied, wall material isdeposited on the at least one layer. The wall material may be applieddirectly to a surface of the at least one layer or may be on (e.g.supported by but not directly in contact with) the at least one layer.The wall material may for example be applied to an area of the outersurface of the coating which may have been treated to improve adhesionbetween the surface and the wall material. The wall material may then bepatterned to form at least one wall for confining the first fluid to adisplay area of the second support plate. The wall material may be SU8and the patterning may therefore be performed using an appropriatephotoresist technique as the skilled person will readily understand.

In some examples the protrusion comprises an electrode such as the thirdelectrode described above. Therefore, in such examples, the depositing afurther layer (for example the protrusion precursor layer) stage of themethod includes depositing a further layer of material for beingpatterned to form part of the protrusion as an electrode.

With one support plate such as the second support plate now beingmanufactured, a further support plate, for example the first supportplate is formed. This involves for example depositing at least one layeron a further substrate and patterning a layer of the at least one layeron the further substrate to form a further electrode. Thus, a similarsupport plate to that just described as being manufactured may be formedwith the wall structures but without the protrusion. Then the firstfluid is dispensed on a surface of the first support plate (though inother examples where the first support plate comprises the protrusionthe first fluid may instead be dispensed on a surface of the secondsupport plate) using for example a dosing technique known to the skilledperson. The second fluid is also dispensed, for example in a containerin which the first and second support plates are immersed when beingjoined together. Then the first and second support plates (in thisexample the further support plate and the support plate having theprotrusion) are adjoined with the first and second fluids being locatedbetween the support plates. This adjoining may be done using for examplean adhesive seal provided at an outermost perimeter of an array of thedisplay elements. This manufacture technique is simple as knowntechniques can be used. Plus, although in the final manufactured devicethe first fluid may adjoin both the surface of the protrusion and thesurface of the support plate, during manufacture the first fluid cansimply be dispensed on the surface of one of the support plates such asthe first support plate, for then being transferred to adjoin theprotrusion surface after manufacture.

The above examples are to be understood as illustrative examples.Further examples are envisaged.

For example, in some examples, the protrusion may be formed as part of awall for substantially confining the first fluid to adjoin a displayarea of the surface of the first support plate, rather than theprotrusion being laterally separated from the wall by the first and/orsecond fluid. In such examples the wall may extend from the firstsupport plate to the second support plate and the protrusion formed aspart of the wall may also extend from one support plate to the other, toact as a conduit or a path for the first fluid to flow to the surface ofthe first support plate. The protrusion as part of a wall does notextend across a whole surface of a wall adjoined by one of the first orsecond fluids. Instead, the protrusion forms a narrow, for exampleelongate, area on the wall surface of a different wettability for thefirst fluid than the rest of the wall surface. The wall may therefore bepredominantly hydrophilic but the protrusion has for example a morewettable surface for the first fluid in the absence of an appliedvoltage. In such examples the second fluid may not be reflective but mayinstead be substantially transmissive for visible light by for exampletransmitting 50% or more of visible light incident on the second fluid.

It is to be understood that any feature described in relation to any oneexample may be used alone, or in combination with other featuresdescribed, and may also be used in combination with one or more featuresof any other of the examples, or any combination of any other of theexamples. Furthermore, equivalents and modifications not described abovemay also be employed without departing from the scope of theaccompanying claims.

What is claimed is:
 1. An electrowetting display device comprising: afirst support plate comprising: a first surface; and a first electrode;a second support plate; at least one of the first support plate or thesecond support plate comprising a protrusion having a second surface,the protrusion having an elongate shape extending from a respective oneof the first support plate or the second support plate towards arespective other of the first support plate or the second support plate;a first fluid in adjoinment with at least one of the second surface orthe first surface; a second fluid immiscible with the first fluid, thefirst fluid and the second fluid located between the first support plateand the second support plate; a second electrode in electrical contactwith the second fluid; and a third electrode, wherein at least one ofthe protrusion, the first support plate or the second support platecomprises the third electrode, wherein a configuration of the firstfluid and the second fluid is switchable, using a voltage appliedbetween at least two of the first electrode, the second electrode or thethird electrode, between: a first configuration with: a first volume ofthe first fluid in adjoinment with the second surface; and a secondvolume of the first fluid in adjoinment with the first surface, and asecond configuration with: a third volume of the first fluid inadjoinment with second surface, the third volume less than first volume;and a fourth volume of the first fluid in adjoinment with the firstsurface, the fourth volume greater than the second volume.
 2. Theelectrowetting display device according to claim 1, the second supportplate comprising the protrusion, wherein the protrusion is not incontact with the first surface.
 3. The electrowetting display deviceaccording to claim 2, wherein the first fluid is transferrable fromadjoinment with the second surface to adjoinment with the first surface,across a distance between the protrusion and the first surface, thedistance corresponding to at least one of: a wettability for the firstfluid of the second surface; a wettability for the first fluid of thefirst surface; a volume of the first fluid; a magnitude of an appliedvoltage appliable between at least two of the first electrode, thesecond electrode or the third electrode; a viscosity of the first fluid;a surface tension of the first fluid; a viscosity of the second fluid;or a surface tension of the second fluid.
 4. The electrowetting displaydevice according to claim 2, wherein the protrusion is separated fromthe first support plate by at least one of the first fluid or the secondfluid.
 5. The electrowetting display device according to claim 1,wherein the second fluid is substantially reflective for visible light.6. The electrowetting display device according to claim 1, the secondsupport plate comprising the protrusion, wherein the protrusion extendsfrom the second support plate and contacts the first surface.
 7. Theelectrowetting display device according to claim 1, wherein the firstsupport plate comprises at least one wall which substantially confinesthe first fluid to adjoin a display area of the first surface, theprotrusion located within the display area and separated from the atleast one wall by at least one of the first fluid or the second fluid.8. The electrowetting display device according to claim 1, wherein theprotrusion comprises: an elongate structure on a layer of one of thefirst support plate or the second support plate, the elongate structureand a part of the layer covered by a hydrophobic layer, the hydrophobiclayer comprising the second surface.
 9. The electrowetting displaydevice according to claim 8, wherein a thickness of the hydrophobiclayer increases along the protrusion in a direction away from the firstsupport plate.
 10. The electrowetting display device according to claim1, comprising a wall which at least partly substantially confines thefirst fluid to adjoin a display area of the first surface, wherein thewall comprises the protrusion, and the wall extends at least partly fromthe first support plate to the second support plate.
 11. Theelectrowetting display device according to claim 1, the first supportplate comprising the protrusion, wherein the protrusion is not incontact with the second support plate.
 12. The electrowetting displaydevice according to claim 1, wherein the second support plate comprisesthe third electrode and the third electrode overlaps the protrusion. 13.The electrowetting display device according to claim 1, wherein thesecond surface comprises a material which, without a voltage applied,has a lower wettability for the first fluid than the first surface. 14.The electrowetting display device according to claim 1, wherein thefirst surface and the second surface each comprise a material which isat least one of: wettable by the first fluid without a voltage applied,or hydrophobic.
 15. The electrowetting display device according to claim1, the second support plate comprising: the protrusion; and a thirdsurface comprising a material which has, without a voltage applied, alower wettability for the first fluid than the second surface.
 16. Anapparatus comprising: an electrowetting display device comprising: afirst support plate comprising: a first surface; and a first electrode;a second support plate; at least one of the first support plate or thesecond support plate comprising a protrusion having a second surface,the protrusion having an elongate shape extending from a respective oneof the first support plate or the second support plate towards arespective other of the first support plate or the second support plate;a first fluid in adjoinment with at least one of the second surface orthe first surface; a second fluid immiscible with the first fluid, thefirst fluid and the second fluid located between the first support plateand the second support plate; a second electrode in electrical contactwith the second fluid; and a third electrode, wherein at least one ofthe protrusion, the first support plate or the second support platecomprises the third electrode, wherein a configuration of the firstfluid and the second fluid is switchable, using a voltage appliedbetween at least two of the first electrode, the second electrode or thethird electrode, between: a first configuration with: a first volume ofthe first fluid in adjoinment with the second surface; and a secondvolume of the first fluid in adjoinment with the first surface, and asecond configuration with: a third volume of the first fluid inadjoinment with the second surface, the third volume less than the firstvolume; and a fourth volume of the first fluid in adjoinment with thefirst surface, the fourth volume greater than the second volume;processor circuitry; and memory circuitry operable to with the processorcircuitry, control switching of the configuration of the first fluid andthe second fluid.
 17. The apparatus of claim 16, the second supportplate comprising the protrusion, wherein the protrusion is not incontact with the first surface.
 18. The apparatus of claim 16, whereinthe second fluid is substantially reflective for visible light.
 19. Theapparatus of claim 16, the second support plate comprising theprotrusion, wherein the protrusion extends from the second support plateand contacts the first surface.
 20. The apparatus of claim 16, whereinthe protrusion comprises: an elongate structure on a layer of one of thefirst support plate or the second support plate, the elongate structureand a part of the layer covered by a hydrophobic layer, the hydrophobiclayer comprising the second surface.
 21. The apparatus of claim 16, thefirst support plate comprising the protrusion, wherein the protrusion isnot in contact with the second support plate.
 22. The apparatus of claim16, wherein the second surface comprises a material which, without avoltage applied, has a lower wettability for the first fluid than thefirst surface.
 23. An electrowetting display device comprising: a firstsupport plate comprising: a first surface; a first electrode; and atleast one wall which substantially confines the first fluid to adjoin adisplay area of the first surface; a second support plate, at least oneof the first support plate or the second support plate comprising aprotrusion having a second surface, the protrusion having an elongateshape which extends from a respective one of the first support plate orthe second support plate towards a respective other of the first supportplate or the second support plate; a first fluid in adjoinment with atleast one of the second surface or the first surface; a second fluidimmiscible with the first fluid, the first fluid and the second fluidlocated between the first support plate and the second support plate; asecond electrode in electrical contact with the second fluid; and athird electrode, wherein at least one of the protrusion, the firstsupport plate or the second support plate comprises the third electrode,wherein the protrusion is located within the display area and isseparated from the at least one wall by at least one of the first fluidor the second fluid, a configuration of the first fluid and the secondfluid switchable using a voltage applied between at least two of thefirst electrode, the second electrode or the third electrode.
 24. Theelectrowetting display device of claim 23, the second support platecomprising the protrusion, wherein the protrusion is not in contact withthe first surface.
 25. The electrowetting display device of claim 23,the first support plate comprising the protrusion, wherein theprotrusion is not in contact with the second support plate.